This invention relates to textile spinning machines, particularly to an open-end spinning rotor cup having a superior hard and wear-resistant surface, and a method of making it by electrolytic deposition.
Textile spinning machines commonly have as an important part an open end spinning rotor cup whose purpose is to collect fibers into strands and impart a twist to form a yarn. See the spinning rotor 9 described in Pfeifer""s U.S. Pat. No. 4,339,014, issued in 1982, Lindner""s U.S. Pat. No. 5,694,756 and Winzen""s U.S. Pat. No. 5,987,871. As spinning machines have become more efficient and productive, the spinning rotors have been caused to rotate ever faster and to process greater and greater quantities of fiber. Workers in the art have had to continuously improve the surface hardness of the rotors to overcome the tendency of the surfaces to wear. While some early spinning rotors had rotational speeds of 30,000 rotations per minute (rpm), a contemporary competitive rotor will turn at the rate of 125,000 rpm or higher and process a wide variety of fibers. See the discussion of static and other problems caused by high rpm, at least with some materials, as described by Coenen in U.S. Pat. No. 6,006,510. The fiber sliding wall, collecting groove and adjacent annular surface of the spinning rotor are subject to continual wear (see the discussion in Wassenhoven""s U.S. Pat. No. 6,047,538), and have been covered with various coatings to prolong the life of the rotor. The problem persists, however, as the machines are pushed to ever higher production rates.
Rotor elements were initially fabricated from aluminum or aluminum alloys, primarily because of the light weight of the aluminum, which is considered desirable for the lesser inertia to overcome during braking. A good review of the braking problem may be found in Wassenhoven et al U.S. Pat. No. 5,964,084; see also U.S. Pat. No. 5,987,872. But unprotected aluminum soon gave way in the past to hardcoat anodizing, and this in turn was found deficient as greater production demands necessitated a more durable material. Because of the difficulty of finding an improved surface for aluminum, workers turned to steel in spite of its greater density and weight. Miyamoto et al, in U.S. Pat. No. 4,502,273 describe thermally hardening selected areas of the rotor using a laser beam.
Thermal hardening of the steel facilitated coating of the steel with nickel to improve wear resistance, but in spite of constantly improving rotor specifications, wear was not eliminated. Some workers in the art attempted to return to aluminum with various ceramic coatings generally applied by thermal spraying processes. While some of these coatings have been successful, adherence of the coating to aluminum is difficult to achieve. Even if the application of a thermally sprayed coating is successful, subsequent finishing to achieve a smooth surface so as to allow proper fiber and/or yarn contact and acceptable composition in the finished product is a costly and difficult process.
The reader may be interested in the ceramic cap described for a navel used in combination with the rotor, in Mackey et al U.S. Pat. Nos. 5,437,147 and 5,475,974.
Contemporary machines commonly use rotor speeds in the range of 120,000 to 125,000 rpm; many of the rotors are made of steel, with composite diamond coatings, boride treatments with zinc or nickel overcoats, and/or, finally, steel rotor elements with boride treatment and composite diamond overcoating. See Schuermann et U.S. Pat. Nos. 6,062,015 and 6,123,989; a coating method is described in the latter patent.
In view of the preference of the industry for a light weight rotor, an aluminum rotor is needed having surface protection effective for long periods at high rpm""s.
We have developed a new hard, wear-resistant spinning rotor. The present invention provides an improved open-end spinning rotor element providing a lightweight rotor cup protected from wear on its critical surfaces by a ceramic material, preferably of a particular composition. The rotor cup element comprises an aluminum body and a ceramic layer over substantially its entire surface or selected portions of the surface, especially the internal surface. The ceramic layer is formed by conversion of the aluminum surface to a hard, wear resistant ceramic by a microarc oxidation process employing an electrolyte and controlled high voltage alternating current to create a plasma discharge at the interface between the aluminum rotor element and the electrolyte.
In U.S. Pat. No. 5,616,229, Samsonov and Hiterer propose the formation of ceramic coatings of up to 300 microns thick within about 90 minutes through the use of an alternating current of at least 700 volts having a shaped wave (not the conventional sinusoidal form) which rises from zero to its maximum height and falls to below 40% of its maximum height within less than a quarter of its full alternating cycle, thereby causing dielectric breakdown, the alternating current being imposed on an electrolytic bath in which the metal subject is an electrode, the bath comprising initially an alkali metal hydroxide and in a later step including an oxyacid salt of an alkali metal, such as sodium tetrasilicate. While the ""229 patent speaks of forming coatings on aluminum surfaces, the authors do not treat the possible use of such a coating process for application to the unique contours of aluminum spinning rotors.
The oxide ceramic coatings utilized according to this invention on the surface of spinning rotors exhibit surface hardnesses of at least 1000 Kn100 and preferably 1300 Kn100 or more, and a density greater than 90% of theoretical, preferably greater than 97%, and a surface roughness after finishing that ranges from 4 to 60 Ra. While aluminum spinning rotor cups are preferred in our invention, we may also use spinning rotors fabricated from titanium, magnesium, beryllium, hafnium, zirconium, and alloys of these with or without aluminum, prepared with coatings of the hardnesses and densities described above.
We use a modified shaped-wave electrolytic process to form a hard coating on the spinning rotor. The process may use the teachings of U.S. Pat. No. 5,616,229 and accordingly that patent is hereby incorporated by reference, in its entirety, into this disclosure. However, the ""229 patent uses two distinct electrolytic baths for the substrates discussed, and we have found it is not necessary to do so for spinning rotors, particularly of aluminum.
Our method comprises forming a hard coating on the incipient spinning rotor cup by immersing it first in an electrolytic bath comprising (deionized) water, an alkali metal salt or hydroxide (preferably potassium hydroxide) as an electrolytic agent, at a concentration of 0.5-7 grams per liter, and, as a passivating agent, a colloidal suspension of sodium silicate in the form Na2Oxc2x7xSiO2 (x= greater than 2.55 by weight) at a concentration of 2.0-9.5 grams per liter while conducting through the bath a modified shaped-wave alternating electric current from a source of at least 250-800 volts through the surface of the incipient spinning rotor cup. The modified shaped-wave electric current rises from zero to its maximum height and falls to below 40% of its maximum height (amplitude) within less than a quarter of a full alternating cycle, thereby causing dielectric breakdown and the formation of a compact ceramic film on the spinning rotor surface.
Thus our invention is seen to include a method of forming a hard ceramic surface on a selected portion of the internal annular surface of a spinning rotor cup comprising (a) placing the spinning rotor cup in an electrolyte bath containing ingredients capable of forming a hard ceramic surface by electrolysis (b) connecting the spinning rotor cup to a source of electric current (c) placing an electrode inside the spinning rotor cup, said electrode being shaped and placed to provide a peripheral terminus substantially peripherally equidistant from the selected portion of internal annular surface, and (d) passing a current through the electrode, the bath, and the rotor cup sufficient to form a hard ceramic coating on the selected internal annular or other surface.
We have developed a special electrode for use in the process, and deploy it in the bath in a particular manner with respect to the spinning rotor cup in order to direct the flow of electrical current to those surfaces subject to a high degree of wear during operation of the spinning rotor.
Thus our invention includes making a wear-resistant spinning rotor cup comprising forming a hard coating on an interior surface of an incipient spinning rotor cup by (i) immersing the incipient spinning rotor in an electrolytic bath comprising a passivating agent and an electrolytic agent, and (ii) passing a modified shaped-wave alternating electric current from a source of 250 to 800 volts through the interior surface of said incipient spinning rotor, wherein the modified shaped-wave electric current rises from zero to its maximum height and falls to below 40% of its maximum height within less than a quarter of a full alternating cycle thereby causing dielectric breakdown and the formation of a ceramic coating on the interior surface, and removing the incipient spinning rotor cup from the electrolytic bath. Preferably, the electrode will have a peripheral terminus and be positioned centrally within the incipient spinning rotor cup so that the terminus is peripherally substantially equidistant from the at least one selected portion of the interior surface of the incipient spinning rotor cup.